GB2380432A - A emission control system for an engine and method therefor. - Google Patents

A emission control system for an engine and method therefor. Download PDF

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Publication number
GB2380432A
GB2380432A GB0213308A GB0213308A GB2380432A GB 2380432 A GB2380432 A GB 2380432A GB 0213308 A GB0213308 A GB 0213308A GB 0213308 A GB0213308 A GB 0213308A GB 2380432 A GB2380432 A GB 2380432A
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Prior art keywords
value
engine operating
device
engine
operating condition
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GB0213308A
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GB0213308D0 (en )
GB2380432B (en )
Inventor
David George Farmer
Gopichandra Surnilla
Michael John Cullen
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Ford Global Technologies LLC
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Ford Global Technologies LLC
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Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0828Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
    • F01N3/0842Nitrogen oxides
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/009Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/009Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
    • F01N13/0093Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series the purifying devices are of the same type
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D41/00Electrical control of supply of combustible mixture or its constituents
    • F02D41/02Circuit arrangements for generating control signals
    • F02D41/021Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • F02D41/027Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus
    • F02D41/0275Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus the exhaust gas treating apparatus being a NOx trap or adsorbent
    • F02D41/028Desulfurisation of NOx traps or adsorbent
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D41/00Electrical control of supply of combustible mixture or its constituents
    • F02D41/02Circuit arrangements for generating control signals
    • F02D41/14Introducing closed-loop corrections
    • F02D41/1438Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1439Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the position of the sensor
    • F02D41/1441Plural sensors
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D41/00Electrical control of supply of combustible mixture or its constituents
    • F02D41/02Circuit arrangements for generating control signals
    • F02D41/14Introducing closed-loop corrections
    • F02D41/1438Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/146Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an NOx content or concentration
    • F02D41/1461Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an NOx content or concentration of the exhaust gases emitted by the engine
    • F02D41/1462Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an NOx content or concentration of the exhaust gases emitted by the engine with determination means using an estimation
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2570/00Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
    • F01N2570/04Sulfur or sulfur oxides
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2570/00Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
    • F01N2570/14Nitrogen oxides
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D41/00Electrical control of supply of combustible mixture or its constituents
    • F02D41/30Controlling fuel injection
    • F02D41/38Controlling fuel injection of the high pressure type
    • F02D2041/389Controlling fuel injection of the high pressure type for injecting directly into the cylinder
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D2200/00Input parameters for engine control
    • F02D2200/02Input parameters for engine control the parameters being related to the engine
    • F02D2200/08Exhaust gas treatment apparatus parameters
    • F02D2200/0808NOx storage capacity, i.e. maximum amount of NOx that can be stored on NOx trap
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D2200/00Input parameters for engine control
    • F02D2200/02Input parameters for engine control the parameters being related to the engine
    • F02D2200/08Exhaust gas treatment apparatus parameters
    • F02D2200/0818SOx storage amount, e.g. for SOx trap or NOx trap
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D41/00Electrical control of supply of combustible mixture or its constituents
    • F02D41/02Circuit arrangements for generating control signals
    • F02D41/14Introducing closed-loop corrections
    • F02D41/1438Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/1446Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being exhaust temperatures
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02ATECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection
    • Y02A50/20Air quality improvement or preservation
    • Y02A50/23Emission reduction or control
    • Y02A50/234Physical or chemical processes, e.g. absorption, adsorption or filtering, characterised by the type of pollutant
    • Y02A50/2344Nitrogen oxides [NOx]

Abstract

A method for controlling an engine which exhausts through an emission control device and which is operable in a plurality of operating conditions including a sulphur purging condition, the method comprises determining a first value representing an amount of SO x accumulated in the emission control device, determining a second value representing an amount of a selected component of the engine exhaust gas stored in the emission control device as a function of the first value and selecting an operating condition as a function of this second value. A third value, representing the remaining storage capacity of the emission control device may be calculated as a function of the first value. The sulphur purge may be initiated when a threshold value for either the accumulated SO x or remaining NO x storage capacity is reached. Determining the first value may include factoring in the air/fuel ratio and the temperature of the emission control device at a given instant. The value representing the amount of SO x accumulated in the emission control device may be reset to zero upon completion of the sulphur purge.

Description

- 1 - A METHOD AND SYSTEM FOR CONTROLLING

AN EMISSION CONTROL DEVICE

The invention relates to a method and system for 5 controlling an emission control device and in particular to a method and system for controlling the nominal storage and release times used in connection with an emission control device to facilitate "lean-burn" operation of an internal combustion engine.

Generally, the operation of a vehicles internal combustion engine produces engine exhaust gas that includes a variety of constituents, including carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). The rates at 15 which the engine generates these constituents are dependent upon a variety of factors, such as engine operating speed and load, engine temperature, spark timing, and EGR.

Moreover, such engines often generate increased levels so of one or more exhaust gas constituents, such as NOx, when the engine is operated in a lean-burn cycle, i.e., when engine operation includes engine operating conditions characterized by a ratio of intake air to injected fuel that is greater than the stoichiometric air-fuel ratio (a "lean" 25 engine operating condition), for example, to achieve greater vehicle fuel economy.

In order to control these vehicle tailpipe emissions, the prior art teaches vehicle exhaust treatment systems that

30 employ one or more three-way catalysts, also referred to as emission control devices, in an exhaust passage to store and release select exhaust gas constituents, such as NOx, depending upon engine operating conditions.

35 For example, U.S. Patent No. 5,437,153 teaches an emission control device which stores exhaust gas NOx when the exhaust gas is lean, and releases previously-stored NOx

- 2 when the exhaust gas is either stoichiometric or ''rich" of stoichiometric, i.e., when the ratio of intake air to injected fuel is at or below the stoichiometric air-fuel ratio. Such systems often employ open-loop control of device storage and release times (also respectively known as device "fill" and "purge" times) so as to maximize the benefits of increased fuel efficiency obtained through lean engine 10 operation without concomitantly increasing tailpipe emissions as the device becomes "filled." The timing of each purge event must be controlled so that the device does not otherwise exceed its NOx storage capacity, because NOx would then pass through the device and effect an increase in is tailpipe NOx emissions. The frequency of the purge is preferably controlled to avoid the purging of only partially filled devices, due to the fuel penalty associated with the purge event's enriched air-fuel mixture.

to It is known from the prior art that the storage

capacity of a given emission control device for a selected exhaust gas constituent is itself a function of many variables, including device temperature, device history, sulphation level, and the presence of any thermal damage to 25 the device. Moreover, as the device approaches its maximum capacity, the prior art teaches that the incremental rate at

which the device continues to store the selected exhaust gas constituent may begin to fall.

so Accordingly, U.S. Patent No. 5,437,153 teaches use of a nominal NOxstorage capacity for its disclosed device which is significantly less than the actual NOx-storage capacity of the device, to thereby provide the device with a perfect instantaneous NOx-retaining efficiency, that is, so that the s device is able to store all engine-generated NOx as long as the cumulative stored NOx remains below this nominal capacity. A purge event is scheduled to rejuvenate the

device whenever accumulated estimates of engine-generated NOx reach the device's nominal capacity.

The amount of the selected constituent gas that is 5 actually stored in a given emission control device during vehicle operation depends on the concentration of the selected constituent gas in the engine feedgas, the exhaust flow rate, the ambient humidity, the device temperature, and other variables including the "poisoning" of the device with lo certain other constituents of the exhaust gas.

For example, when an internal combustion engine is operated using a fuel containing sulphur, the prior art

teaches that sulphur may be stored in the device and may 15 correlatively cause a decrease in both the device's absolute capacity to store the selected exhaust gas constituent, and the device's instantaneous constituent-storing efficiency.

When such device sulphation exceeds a critical level, 20 the stored SOx must be "burned off" or released during a de-

sulphation event, during which device temperatures are raised above perhaps about 650 C in the presence of excess HC and CO.

25 U.S. Patent No. 5,746,049 teaches a device de sulphation method which includes raising the device temperature to at least 650 C by introducing a source of secondary air into the exhaust upstream of the device when operating the engine with an enriched air-fuel mixture and so relying on the resulting exothermic reaction to raise the device temperature to the desired level to purge the device of SOx.

Thus, it will be appreciated that both the device s capacity to store the selected exhaust gas constituent, and the actual quantity of the selected constituent stored in the device, are complex functions of many variables that

prior art accumulation-model-based systems do not take into

account. It is an object of this invention to provide a method 5 and system for controlling an internal combustion engine whose exhaust gas is received by an emission control device which can more accurately determine the amount of the selected exhaust gas constituent stored in an emission control device during lean engine operation and which, in lo response, can more closely regulate device fill and purge times to optimize tailpipe emissions.

According to a first aspect of the invention there is provided a method for controlling an engine, wherein the 15 engine is operative at a plurality of engine operating conditions, including a de-sulphating engine operating condition, characterized by combustion of air-fuel mixtures lean and rich of a stoichiometric air-fuel mixture, and wherein exhaust gas generated by such combustion is directed 20 through an emission control device that stores a selected exhaust gas constituent when the exhaust gas is lean and releases the stored selected constituent when the exhaust gas is rich, the method comprising determining a first value representing an amount of SOx accumulated in the device; 25 determining a second value representing an amount of the selected constituent currently stored in the device as a function of the first value and selecting an engine operating condition as a function of the second value.

30 Determining the first value may include accumulating an instantaneous value representative of an incremental amount of accumulated SOx during an engine operating condition characterized by an air-fuel mixture that is not richer than a stoichiometric air-fuel mixture.

5 - The instantaneous value may be adjusted based on at least one of an instantaneous air-fuel ratio and an instantaneous device temperature.

5 The method may include resetting the first value to zero when selecting the de-sulphating engine operating condition. The first value may be determined as a function of the lo instantaneous fuel flow rate during engine operating conditions no richer than a stoichiometric engine operating condition. The method may further include determining a third 15 value representing a current capacity of the device to store the selected constituent as a function of the first value; and wherein selecting includes comparing the second value to the third value.

so Selecting an engine operating condition may further include comparing the first value with a predetermined threshold value.

The de-sulphating engine operating condition may be 25 selected when the first value exceeds the predetermined threshold value.

According to a second aspect of the invention there is provided a system for controlling an engine, wherein the so engine is operative at a plurality of engine operating conditions, including a de-sulphating engine operating condition, characterized by combustion of air-fuel mixtures lean and rich of a stoichiometric air-fuel mixture, and wherein exhaust gas generated by such combustion is received 35 by an emission control device that stores a selected exhaust gas constituent when the exhaust gas is lean and releases the stored selected constituent when the exhaust gas is rich

wherein the system comprises of a controller including a microprocessor arranged to determine a first value representing an amount of SOx accumulated in the device and to determine a second value representing an amount of the 5 selected constituent currently stored in the device as a function of the first value, the controller being further arranged to select an engine operating condition as a function of the second value.

lo The controller may be further arranged to accumulate an instantaneous value representative of an incremental amount of accumulated SOx during an engine operating condition characterized by an air-fuel mixture that is not richer than a stoichiometric air-fuel mixture.

The controller may be further arranged to adjust the instantaneous value based on at least one of an instantaneous air-fuel ratio and an instantaneous device temperature. The controller may be further arranged to reset the first value to zero when selecting the de-sulphating engine operating condition.

25 The controller may be further arranged to determine the first value as a function of the instantaneous fuel flow rate during engine operating conditions no richer than a stoichiometric engine operating condition.

30 The controller may be further arranged to determine a third value representing a current capacity of the device to store the selected constituent as a function of the first value, and wherein the controller is further arranged to compare the second value to the third value.

The invention will now be described by way of example with reference to the accompanying drawing Fig.1.

- 7 Fig.1 shows an exemplary control system 10 for a four-

cylinder gasoline-powered engine 12 for a motor vehicle includes an electronic engine controller 14 having ROM, RAM 5 and a processor ("CPU'') as indicated, as well as an engine-

off timer that provides a value for the elapsed time since the engine 12 was last turned off as a variable, "soak time." lo The controller 14 controls the operation of each of a set of fuel injectors 16 which are of conventional design and are each positioned to inject fuel into a respective cylinder 18 of the engine 12 in precise quantities as determined by the controller 14.

The controller 14 similarly controls the individual operation, i.e., timing, of the current directed through each of a set of spark plugs 20 in a known manner and also controls an electronic throttle 22 that regulates the mass so flow of air into the engine 12.

An air mass flow sensor 24, positioned at the air intake of engine's intake manifold 26, provides a signal regarding the air mass flow resulting from positioning of is the engine's throttle 22. The air flow signal from the air mass flow sensor 24 is utilized by the controller 14 to calculate an air mass value AM which is indicative of a mass of air flowing per unit time into the engine's induction system. A first oxygen sensor 28 coupled to the engine's exhaust manifold detects the oxygen content of the exhaust gas generated by the engine 12 and transmits a representative output signal to the controller 14.

The first oxygen sensor 28 provides feedback to the controller 14 for improved control of the air-fuel ratio of

the air-fuel mixture supplied to the engine 12, particularly during operation of the engine 12 at or about the stoichiometric air-fuel ratio (A = 1.00). A plurality of other sensors, including an engine speed sensor and an 5 engine load sensor, indicated generally at 30, also generate additional signals in a known manner for use by the controller 14.

An exhaust system 32 transports exhaust gas produced o from combustion of an air-fuel mixture in each cylinder 18 through a pair of emission control devices 34,36. A second oxygen sensor 40, which may also be a switching-type HEGO sensor, is positioned in the exhaust system 32 between the first and second devices 34,36. A third oxygen sensor 42, 15 which likewise is a switching-type HEGO sensor, is positioned downstream of the second device 36.

A temperature sensor generates a signal representing the instantaneous temperature T of the second device 36, 20 also useful in optimizing device performance as described more fully below.

Upon commencing lean engine operation, the controller 14 adjusts the output of the fuel injectors 16 to thereby 25 achieve a lean air-fuel mixture for combustion within each cylinder 18 having an air-fuel ratio greater than about 1.3 times the stoichiometric air-fuel ratio. For each subsequent background loop of the controller 14 during lean

engine operation, the controller 14 determines a value 30 representing the instantaneous rate FG_NOX_RATE at which NOx is being generated by the engine 12 as a function of instantaneous engine operating conditions, which may include, without limitation, engine speed, engine load, air-

fuel ratio, EGR, and spark.

By way of example only the controller 14 retrieves a stored estimate FG_NOX_RATE for the instantaneous NOx

generation rate from a lookup table stored in ROM based upon sensed values for engine speed N and engine load LOAD, wherein the stored estimates FG_NOX_RATE are originally obtained from engine mapping data.

During a first engine operating condition, characterized by combustion in the engine 12 of a lean air-

fuel mixture, the controller 14 determines a value FG_NOX_RATE representing the instantaneous rate, in grams 0 per-hour, at which NOx is being generated by the engine 12, preferably expressed by the following relationship: FG_NOX_RATE = FNXXX1(N,LOAD)*FNXXA()*FNXXB(EGRACT)

*FNXXC(SPK_DELTA)*FMXXD(ECT-200)

where: FNXXX1(N,LOAD) is a lookup table containing NOx emission rate values, in grams-per-hour, for current engine 20 speed N and engine load LOAD; FNXXA (A) is a lookup table for adjusting the FG_NOX RATE value for air-fuel ratio which inherently adjusts the FG_NOX_RATE value for barometric pressure; FNXXB(EGRACT) is a lookup table for adjusting the FG NOX_RATE value for actual exhaust gas recirculation percentage; 30 FNXXC(SPK_DELTA) is a lookup table for adjusting the FG_NOX_RATE value for the effect of knock sensor or hot open-loop induced spark retard, with NOx production being reduced with greater spark retard; and 35 FMXXD(ECT-200) is a lookup table for adjusting the FG_NOX_RATE value for the effect of engine coolant temperature above 93 C (200 F).

Preferably, the determined feedgas NOx rate FG_NOX_RATE is further modified to reflect any reduction in feedgas NOx concentration upon passage of the exhaust gas through the 5 first device 34, as through use of a ROM-based lookup table of three-way catalyst efficiency in reducing NOx as a function of the current air-fuel ratio X, to obtain an adjusted instantaneous feedgas NOx rate ADJ_FG_NOX_RATE.

10 The controller 14 also calculates an instantaneous value INCREMENTAL_NOX_RATE representing the incremental rate at which NOx is stored in the second device 36 during each background loop (e.g., ti,j) executed by the controller 14

during a given lean operating condition, in accordance with 15 the following formula: INCREMENTAL_NOX_RATE = ADJ_FG_NOX_RATE

* FNNXRT_EFF(T,TOTAL_NOX)

* FNSX_EFF(SOX_GRAMS),

20 where: ADJ_FG_NOX_RATE = adjusted instantaneous feedgas NOx rate FNNXRT_EFF(T,TOTAL_NOX) represents a lookup table for instantaneous device efficiency based on instantaneous device temperature T and a current value representing a cumulative amount TOTAL_NOX of NOx which has previously been stored in the second device 36 during a given lean engine operating condition, as described more fully below; and FNSX_EFF(SOX_GRAMS) represents an empirically established capacity modifier which varies as a function of a current value SOX_GRAMS representing an amount of SOx which has accumulated within the second device 36 since a 35 prior de-sulphating event, the value SOX_GRAMS being itself determined based on fuel flow, as described more fully below.

The controller 14 thereafter updates a stored value TOTAL_NOX representing the cumulative amount of NOx which has been stored in the second device 36 during the given 5 lean operating condition, in accordance with the following formula: TOTAL_ NOXn = TOTAL_NOX(nl) + INCREMENTAL_NOX_RATE * ti,j loThe controller 14 then determines a suitable value NOX_CAP representing the instantaneous NOx-storage capacity of the second device 36.

By way of example only the value NOX_CAP varies as a 15 function of second device temperature T. a determined value FNSX_CAP representing the amount of accumulated SOx, and a determined value PERMANENT_AGING representing an adjustment of NOx-storing capacity due to thermal aging and penetrated sulphur (which cannot otherwise be purged from the second 20 device 36 during a de-sulphation event).

More specifically, in a preferred embodiment, the instantaneous NOxstorage capacity value NOX_CAP is calculated in accordance with the following formula: NOX_CAP = NOX_PURGE * FNNX_CAP(T) * FNSX_CAP(SOX_GRAMS) * PERMANENT_AGING

where: so NOX_PURGE is a predetermined threshold value for second device NOx-storage capacity; FNNX_CAP(T) represents an empirically established capacity modifier which varies as a function of second as device temperature T;

FNSX_EFF(SOX_GRAMS) represents an empirically established capacity modifier which varies as a function of the current value SOX_GRAMS representing an amount of SOx which has accumulated within the second device 36 since a 5 prior de-sulphating event; and PERMANENT_AGING represents an empirically established capacity modifier which varies as a function of thermal aging and permanent sulphation of the second device 36.

The controller 14 then compares the updated value TOTAL_NOX representing the cumulative amount of NOx stored in the second device 36 with the determined value NOX_CAP representing the second device's instantaneous NOx-storage 5 capacity. The controller 14 discontinues the given lean operating condition and schedules a purge event when the updated value TOTAL_NOX exceeds the determined value NOX_CAP.

20 As noted above, the controller 14 determines values for FNSX_EFF and FNSX_CAP based upon the current value SOX_GRAMS representing the amount of SOx which has accumulated in the second device 36 since the last desulphation event, during both lean and stoichiometric engine operating conditions.

In accordance with another feature of the invention, the controller 14 determines the current value SOX_GRAMS by determining a value DELTA_SOX representing an instantaneous amount of SOx which is being added to the second device 36 30 during a given background loop time ti,j, using the

following formula: DELTA_SOX = FNSOXFUEL(FUELFLOW_MFA AM,A,Li,j) * FNSOXADJ(A,T) r ti' j 3 5 where:

- 13 FUELFLOW_MFA represents a calculated value for current fuel flow rate based on current air mass flow AM, the current air-fuel ratio A, and the background loop time ti,j;

5 FNSOXFUEL(FUELFLOW_MFA) represents an empirically established generatedSOx modifier which varies as a function of the current fuel flow rate FUELFLOW_MFA; and FNSOXADJ(A,T) represents an empirically established 10 generated-SOx modifier which varies as a function of both the current airfuel ratio A and the instantaneous second device temperature T. The controller 14 thereafter updates a stored value 5 SOX_GRAMS representing the cumulative amount of SOx which has accumulated in the second device 36 since the last de-

sulphation event, in accordance with the following formula: SOX_GRAMSn = SOX_GRAMS (n-l) + DELTA_SOX.

In accordance with a further benefit of the invention, the current value SOX_GRAMS is also used to schedule a de-

sulphation event. Specifically, the controller 14 compares the current value SOX_GRAMS to a predetermined threshold 25 value SOX_MAX_GRAMS. The controller 14 schedules a de-

sulphation event when the current value SOX_GRAMS exceeds the predetermined threshold value SOX_MAX_GRAMS.

The invention therefore provides a method for So controlling the fill and purge cycle of an emission control device disposed in an exhaust treatment system for an internal combustion engine. Under the invention, values representing an instantaneous rate at which a selected constituent of the engine-generated exhaust gas, such as 35 NOx, is stored in the device, and the instantaneous capacity of the device to store the selected constituent, are determined as a function of a calculated value representing

- 14 an amount of SOx which has been accumulated in the device since an immediately prior de-sulphation event. More specifically, in a preferred embodiment, the calculated value representing the amount of accumulated SOx is 5 determined as a function of the instantaneous fuel flow rate during lean and stoichiometric engine operating conditions, preferably further adjusted to reflect the effects of instantaneous air-fuel ratio and instantaneous device temperature on the accumulation of SOx in the device.

In accordance with another feature of the invention the calculated value representing the amount of accumulated SOx is used to schedule a deviceregeneration or "de-sulphation" event. Specifically, the value is preferably compared with 5 a predetermined threshold value, with a desulphating engine operating condition being selected when the calculated accumulated SOx value exceeds the predetermined threshold value. so In accordance with yet another feature of the invention, the values representing the instantaneous storage rate for the selected constituent in the device, and the instantaneous storage capacity, are further determined as a function of a determined value representing a permanent reduction in the constituent storage capacity of the device due to thermal effects and "penetrated" or diffused sulphur which cannot otherwise be purged during a nominal device-de sulphation event.

Claims (18)

- 15 Claims
1. A method for controlling an engine, wherein the engine is operative at a plurality of engine operating 5 conditions, including a de-sulphating engine operating condition, characterized by combustion of air-fuel mixtures lean and rich of a stoichiometric air-fuel mixture, and wherein exhaust gas generated by such combustion is directed through an emission control device that stores a selected lo exhaust gas constituent when the exhaust gas is lean and releases the stored selected constituent when the exhaust gas is rich, the method comprising determining a first value representing an amount of SOx accumulated in the device; determining a second value representing an amount of the 15 selected constituent currently stored in the device as a function of the first value and selecting an engine operating condition as a function of the second value.
2. A method as claimed in claim 1, wherein 20 determining the first value includes accumulating an instantaneous value representative of an incremental amount of accumulated SOx during an engine operating condition characterized by an air-fuel mixture that is not richer than a stoichiometric air-fuel mixture.
3. A method as claimed in claim 2, wherein the instantaneous value is adjusted based on at least one of an instantaneous air-fuel ratio and an instantaneous device temperature.
4. A method as claimed in claim 1 or in claim 2 wherein the method includes resetting the first value to zero when selecting the de-sulphating engine operating condition.
5. A method as claimed in any of claims 1 to 4 wherein the first value is determined as a function of the
- 16 instantaneous fuel flow rate during engine operating conditions no richer than a stoichiometclc engine operating condition. 5
6. A method as claimed in any of claims 1 to 5 further including determining a third value representing a current capacity of the device to store the selected constituent as a function of the first value; and wherein selecting includes comparing the second value to the third lo value.
7. A method as claimed in claim 1, wherein selecting an engine operating condition further includes comparing the first value with a predetermined threshold value.
S. A method as claimed in claim 7, wherein the de-
sulphating engine operating condition is selected when the first value exceeds the predetermined threshold value.
20
9. A system for controlling an engine, wherein the engine is operative at a plurality of engine operating conditions, including a de-sulphating engine operating condition, characterized by combustion of air-fuel mixtures lean and rich of a stoichiometric air-fuel mixture, and 25 wherein exhaust gas generated by such combustion is received by an emission control device that stores a selected exhaust gas constituent when the exhaust gas is lean and releases the stored selected constituent when the exhaust gas is rich wherein the system comprises of a controller including a so microprocessor arranged to determine a first value representing an amount of SOx accumulated in the device and to determine a second value representing an amount of the selected constituent currently stored in the device as a function of the first value, the controller being further 35 arranged to select an engine operating condition as a function of the second value.
10. A system as claimed in claim 9 wherein the controller is further arranged to accumulate an instantaneous value representative of an incremental amount of accumulated SOx during an engine operating condition 5 characterized by an air-fuel mixture that is not richer than a stoichiometric air-fuel mixture.
11. A system as claimed in claim 10 wherein the controller is further arranged to adjust the instantaneous lo value based on at least one of an instantaneous air-fuel ratio and an instantaneous device temperature.
12. A system as claimed in any of claims 9 to 11 wherein the controller is further arranged to reset the IS first value to zero when selecting the de-sulphating engine operating condition.
13. A system as claimed in any of claims 9 to 12 wherein the controller is further arranged to determine the 20 first value as a function of the instantaneous fuel flow rate during engine operating conditions no richer than a stoichiometric engine operating condition.
14. A system as claimed in any of claims 9 to 13 25 wherein the controller is further arranged to determine a third value representing a current capacity of the device to store the selected constituent as a function of the first value, and wherein the controller is further arranged to compare the second value to the third value.
15. A system as claimed in any of claims 9 to 14 wherein the controller is further arranged to compare the first value with a predetermined threshold value.
is
16. A system as claimed in claim 15, wherein the controller is further arranged to select the de-sulphating
engine operating condition when the first value exceeds the predetermined threshold value.
17. A method substantially as described herein with 5 reference to the accompanying drawing.
18. A method substantially as described herein with reference to the accompanying drawing.
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US6490860B1 (en) 2002-12-10 grant
DE10223984A1 (en) 2003-01-09 application

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